1. Field of the Invention
The invention relates to an apparatus for treating workpieces with fluids in general and for coating hollow bodies in particular.
2. Description of Related Art
Plastics, in particular transparent plastics, are becoming increasingly important, and in many fields are displacing glass as the preferred material.
One such example is drinks bottles, which a few years ago were almost exclusively made from glass but nowadays are to a large extent made from PET plastic. The reason for this is the huge weight saving.
However, plastic bottles may have a number of drawbacks with respect to glass bottles, for example the plastics used, for example PET, are not sufficiently gas-impermeable, and consequently, in particular in the case of beverages containing carbon dioxide, the shelf life is shorter than with glass bottles unless special precautions are taken.
For this reason, the plastic bottles are internally and/or externally provided with a barrier layer by means of PICVD processes, which lengthens the shelf life.
Since drinks bottles are mass-produced products, there is a huge pressure on costs, and consequently there is a perpetual demand for improvements to the coating processes and apparatus used for this purpose.
Consequently, for efficient coating of PET bottles and other workpieces made from dielectric material, preferably plastics, it is desirable to develop an apparatus which allows very short cycle times and therefore a high throughput. Throughputs which are typically required are in the region of 10,000 bottles per hour.
WO 00/58631 has disclosed a machine of this type with a conveyor carousel for the treatment of hollow bodies in which 20 identical treatment stations are arranged on the conveyor carousel.
The invention defined in the abovementioned document works on the basis that the weight and volume of the pumps prevent them from being carried along on the carousel. Consequently, the pumps are in a fixed position and a rotary connection or distributor is used to connect the pumps to the stations.
Furthermore, the 20 stations are divided into two groups, with each group being assigned to an independent, equivalent pressure source, or the groups being differentiated on the basis of the pumps to which they are connected. The rotary distributor determines the times during the rotary motion of the conveyor carousel at which a certain pump is in communication with a certain treatment station, the distributor for this purpose having a rotating ring with 20 openings and a stationary ring with in each case 3 slots for the two groups.
However, this machine has a number of serious drawbacks.
The stationary arrangement of the pumps is disadvantageous, since the distances from the stations to the pump are relatively long, and consequently the pump power is reduced.
Furthermore, dusts or flaked-off coating fragments may accumulate in the evacuation lines and the distributor, which has an adverse effect on sealing and entails high levels of maintenance outlay.
However, a particular drawback is the use of a rotatable distributor with axially arranged disks. Distributors of this type are extremely difficult to seal and are particularly susceptible to faults caused by foreign bodies. Furthermore, on account of the fixed opening arrangement, the distributor does not allow the process sequence to be varied in any way, making it an inflexible concept.